This application is based upon and claims priority of Japanese Patent Application No. 2001-338502, filed on Nov. 2, 2001, the contents being incorporated herein by reference.
The present invention relates to an insulation film material which can form a porous insulation film of high mechanical strength and low dielectric constant, an insulation film, method for forming the insulation film, and a semiconductor device.
Recently, with increased integration degrees and increased element densities of semiconductor integrated circuits, higher layer multiplication of semiconductor elements is increasingly required. Such increased integration of semiconductor integrated circuits increases capacitances among interconnections of semiconductor elements, which lowers signal propagation speed. The interconnection delay in the interconnections has become a conspicuous problem.
So far in the generation of above 1 xcexcm-interconnect ion gaps of semiconductor devices, the interconnection delay has not generally much influenced the devices. However, when the interconnection gaps become below 1 xcexcm as semiconductor integrated circuits are more integrated, the influence of the interconnection delay on the device velocity cannot be bypassed. Especially in circuits which will have interconnection gaps of below 0.5 xcexcm, the interconnection delay caused by parasitic capacities among interconnections will have much influence on the device velocity.
Generally is known that an interconnection delay T is influenced by an interconnection resistance R and an interconnection capacitance C and expressed by the following formula.
Txe2x88x9dCR 
An interconnection capacitance C is expressed by the following formula where an electrode area is represented by S; an interconnection gap, d; vacuum dielectric constant, xcex50; and an interconnection insulation film dielectric constant, xcex5r.   C  =                    ϵ        0            ⁢              ϵ        r            ⁢      S        d  
Thus, in order to reduce the interconnection delay it is found effective means to lower a dielectric constant of the interconnection insulation film.
Conventionally, in semiconductor integrated circuits, materials of the interconnection insulation film have been silicon dioxide SiO2, silicon nitride SiN, phospho silicate glass PSG, etc. have been used. Silicon oxide film, which is the most popular in semiconductor devices, and which is formed by chemical vapor deposition (CVD) has an about 4 of dielectric constant.
Furthermore, for lower dielectric constants of the interconnection insulation film, uses of fluorine-added silicon oxide film (SiOF film) and organic polymers, such as polyimide, etc. are considered. The use of silica-based porous films having a number of pores formed in the films for lower dielectric constants as the interconnection insulation film is considered.
However, SiOF films formed by CVD have dielectric constant values ranging from about 3.3 to 3.5 and it is difficult to form SiOF films of dielectric constant values of below 3. When SiOF films are used as the interconnection insulation film, the interconnection capacitance cannot be sufficiently reduced. SiOF films have high hygroscopicity and often have increased dielectric constants after formed.
On the other hand, organic polymers, such as polyimide, etc. have low dielectric constants ranging from about 2 to 3. However, organic polymers are insufficient in heat resistance and adhesion and have restricted fabrication processes for semiconductor devices.
In the above-described background, in order to realize the required low dielectric constants, silica-based porous film will be prospective. Silica-based porous film has pores formed by applying to a substrate a material including a siloxane resin and a pyrolytic resin and sintering the material.
However, in the silica-based porous film, when a pore volume in the film is increased for lower dielectric constant, the film has the mechanical strength extremely lowered. In order to form a porous film of, e.g., a below 2.0xe2x88x92 dielectric constant, a porosity of the film must be above 50%. Disadvantageously, the film tends to be broken in the processes of chemical mechanical polishing (CMP), etc. The film has also a disadvantage of high hygroscopicity. Accordingly, silica-based porous film cannot have sufficient properties for forming insulation films of low dielectric constants which are essential to realize high-velocity semiconductor devices.
An object of the present invention is to provide an insulation film material which can form a porous insulation film of high mechanical strength and low dielectric constant, an insulation film, method for forming the insulation film, and a semiconductor device.
According to one aspect of the present invention, there is provided an insulation film forming material comprising: a silicon compound having a skeleton of Cxe2x80x94C bonds; a porous forming compound which is decomposed or evaporated by a heat treatment; and a solvent which dissolves the silicon compound with the porous forming material.
According to another aspect of the present invention, there is provided an insulation film comprising a film of a silicon compound having a skeleton containing Cxe2x80x94C bonds, wherein pores of below 10 nm-size are formed in the film.
According to farther another aspect of the present invention, there is provided a method for forming an insulation film comprising the steps of: applying to a substrate an insulation film forming material including a silicon compound having a skeleton containing Cxe2x80x94C bonds, a pore forming compound which is decomposed or evaporated by a heat treatment and a solvent which dissolves the silicon compound and the pore forming compound; drying the insulation film forming material applied to the substrate to form a film containing the silicon compound and the pore forming compound; and decomposing or evaporating the pore forming compound by subjecting the substrate to the heat treatment to eliminate the pore forming compound from the film to form pores in the film.
According to farther another aspect of the present invention, there is provided a semiconductor device comprising a porous insulation film comprising a film of a silicon compound having a skeleton containing Cxe2x80x94C bonds formed on a semiconductor substrate, wherein pores of below 10 nm-size are formed in the film.
As described above, according to the present invention, a porous insulation film is formed of an insulation film forming material including a silicon compound having a skeleton containing Cxe2x80x94C bonds, a pore forming compound which is decomposed or evaporated by a heat treatment, a solvent for dissolving the silicon compound and the pore forming compound, whereby the porous insulation film can have good mechanical strength and low dielectric constant.